In recent years, as a variety of electronic equipments become compact, electronic devices to be installed inside the electronic equipments have become smaller and higher in performance. As one of the electronic devices, there is a ceramic electronic device, such as a CR built-in substrate and a multilayer ceramic capacitor, and the ceramic electronic devices have been required to be smaller and higher in performance.
To pursue a smaller ceramic electronic device having a higher capacitance, there is a strong demand for thinking a dielectric layer. Recently, a thickness of a dielectric green sheet has become about μm or less.
To produce a ceramic green sheet, normally, a ceramic slurry composed of ceramic powder, a binder (an acrylic based resin and a butyral based resin, etc.), a plasticizer (phthalate esters, glycols, adipic acids, and phosphoric esters) and an organic solvent (toluene, MEK (Methyle Ethyle keton) and acetone, etc.) are prepared. Next, the ceramic slurry coated on a carrier film (a carrier film made by PET and PP) by using the doctor blade method, etc. and dried by heating.
Also, a method of producing by preparing a ceramic slurry wherein the ceramic powder and binder are mixed in a solvent, then, 2-Dimensional drawing a film-shaped item obtained by extruding slurry has been considered in recent years.
A method of producing a multilayer ceramic capacitor by using the ceramic green sheet explained above will be explained in detail. An internal electrode conductive paste containing metal powder and a binder is printed to be a predetermined pattern on the ceramic green sheet and dried to form an internal electrode pattern. After that, the green sheet is peeled from the carrier film and stacked by a predetermined number of layers. Here, two methods are proposed, that are a method of peeling the green sheet from the carrier film before stacking in layers and a method of peeling the carrier film after stacking in layers and adhering by compression, but the difference is not large. Finally, the stacked body is cut to be chips, so that green chips are prepared. After firing the green chips, external electrodes are formed, so that a multilayer ceramic capacitor and other electronic devices are produced.
When producing a multilayer ceramic capacitor, an interlayer thickness of sheets formed with internal electrodes is in a range of 3 μm to 100 μm or so based on a desired capacitance required as a capacitor. Also, in a multilayer ceramic capacitor, a part not formed with internal electrodes is formed on an outer part in the stacking direction of the capacitor chip.
In such a multilayer ceramic capacitor, it was general to use a polyvinyl butyral resin having a polymerization degree of 1000 or less (Mw=50,000) as a binder to be used (refer to the patent article 1 below: the Japanese Patent Publication No. 10-67567). As the reasons, to sufficiently secure adhesiveness of ceramic green sheets at the time of stacking, to reduce surface roughness of the green sheets, to secure plasticity of the green sheets, and to reduce viscosity of slurry may be mentioned. As a plasticizer, generally, phthalic acid, adipic acid, sebacic acid, and phosphoric esters can be used, which were selected in terms of a boiling point and hazardous property, etc. in an object of giving plasticity.
In recent years, as electronic equipments become more compact, electronic devices to be used therein have rapidly become more compact. In multilayer electronic devices as typified by a multilayer ceramic capacitor, rapid development has been made on increasing the number of layers to be stacked and attaining a thinner interlayer thickness. To respond to the technical trends, a thickness of a green sheet, which determines the interlayer thickness, has almost become 3 μm or less to 2 μm or less. Therefore, in a production process of a multilayer ceramic capacitor, it is necessary to handle extremely thin green sheets and to design very advanced green sheet properties.
As characteristics required as the properties of such an extremely thin green sheet, sheet strength, flexibility, smoothness, adhesiveness when being stacked, handlability (electrostatic property), etc. may be mentioned, and balance of a higher order is required.
Note that, as shown in the patent article 2: the Japanese Unexamined Patent Publication No. 6-206756, there is known a technique of using a polyvinyl butyral resin having a polymerization degree of 1000 or more as a binder in green sheet slurry containing an aqueous solvent for a purpose of eliminating a short-circuiting defect.
However, the patent article 2 is not for particularly attaining a thinner organic solvent based green sheet, and a range of a polymerization degree of a polyvinyl butyral resin is not limited to a specified range. Moreover, a butyralation degree and a residual acetyl group amount of the resin are not focused at all.